The present application is a U.S. national application of PCT/IL97/00410, filed Dec. 15, 1997.
The present invention relates to linear motion and to piezoelectric motors generally and more particularly to the use of piezoelectric motors for moving delicate materials, such as paper.
Linear motion and piezoelectric motors are known in the art. SU 693493 describes a piezoelectric motor comprising a flat rectangular piezoelectric plate having one electrode covering essentially all of one large face of the plate (xe2x80x9cthe back facexe2x80x9d) and four electrodes each covering a quadrant of the front face. The back electrode is grounded and the electrodes of the front face are electrically connected on the diagonal. Two ceramic pads are attached to one of the long edges of the plate and these pads are pressed against the object to be moved by a spring mechanism which presses the other long edge.
The long and short edges of the piezoelectric ceramic have similar resonant frequencies (for different mode orders) such that, when one pair of connected electrodes is excited with an alternating current (AC) voltage to which the ceramic is responsive, the object moves in one direction, and when the other pair of electrodes is excited, the object moves in the other direction.
One aspect of the present invention is concerned with the transport of flexible materials such as paper and cloth.
In a preferred embodiment of the invention a piezoelectric motor is used to move the material.
There is thus provided, in accordance with a preferred embodiment of the invention, apparatus for providing linear motion to a generally flat flexible material, comprising:
(a) at least one piezoelectric ceramic motor situated on a first side of the flat flexible material and having a contact surface which contacts the flat flexible material and which imparts said linear motion; and
(b) a bearing surface situated on a second side of the flat flexible material opposite said contact surface.
In one preferred embodiment of the invention the bearing surface is the surface of a roller. In other preferred embodiments of the invention, the bearing surface is a contact surface associated with a second piezoelectric motor.
In these other preferred embodiments of the invention, the bearing surface is a contact surface of a second piezoelectric motor and the second piezoelectric motor also imparts said linear motion to the flat flexible material via said contact surface, preferably the at least one and the second piezoelectric motors both impart linear motion to the flexible material in the same direction.
In one of these other preferred embodiments of the invention, the at least one and second piezoelectric motors impart said linear motion in a given direction during motion periods which alternate with periods during which said motion is not applied and the motion periods of the at least one and the second piezoelectric motors at least partially overlap. Preferably, the motion periods of one of the at least one and the second piezoelectric motors is fully contained within the motion period of the other piezoelectric motor. Preferably, the motion periods of the at least one and the second piezoelectric motors coincide.
Preferably, the contact surfaces of the at least one piezoelectric motor and the second piezoelectric motor are displaced toward the flexible material during their respective periods of motion such that the material is pinched between the respective contact surfaces.
Alternatively the contact surface of the at least one piezoelectric motor is displaced toward the flexible material during the period of motion of the at least one piezoelectric motor and wherein the contact surface of the second piezoelectric motor is displaced away from the flexible material during the period of motion of the at least one piezoelectric motor. Preferably, the contact surface of the second piezoelectric motor is displaced toward the flexible material during the period of motion of the second piezoelectric motor and the contact surface of the at least one piezoelectric motor is displaced away from the flexible material during the period of motion of the second piezoelectric motor, such that the at least one piezoelectric motor and second piezoelectric motor alternately apply motion to the flexible material. While it might be expected that this apparatus would not operate since the flexible material would move from side to side, remaining in contact with both motors and thus not moving at all. However, it appears that even the relatively low mass and stiffness of paper is sufficient to allow for the motors to independently move the material.
In a preferred embodiment of the invention, the at least one piezoelectric motor comprises:
a second contact surface which contacts and is operative to apply linear motion to a second portion of the flexible material;
and further comprising:
a second bearing surface situated on a second side of the flat flexible material opposite said second contact surface.
As with the first bearing surface, the second bearing surface may be a roller or a contact surface of an additional piezoelectric motor. The additional piezoelectric motor preferably cooperates with the second contact surface in the same way as the second piezoelectric motor cooperates with the contact surface.
There is further provided, in accordance with a preferred embodiment of the invention, a method for providing linear motion to a generally flat flexible material, comprising:
(a) contacting a contact surface of at least one piezoelectric ceramic motor with a first side of the flat flexible material, said at least one motor being operative to impart linear motion to surfaces which are in contact with the contact surface; and
(b) providing a bearing surface on a second side of the flat flexible material opposite said contact surface.
In one preferred embodiment of the invention the bearing surface is the surface of a roller. In other preferred embodiments of the invention, the bearing surface is a surface associated with another piezoelectric motor.
In these other preferred embodiments of the invention, the bearing surface is a contact surface of a second piezoelectric motor and wherein the second piezoelectric motor also imparts said linear motion to the flat flexible material via said contact surface, preferably the at least one and the second piezoelectric motors both impart linear motion to the flexible material in the same direction.
In one of these other preferred embodiments of the invention, the at least one piezoelectric motor and the second piezoelectric motor impart said linear motion in a given direction during motion periods which alternate with periods during which said motion is not applied and the motion periods of the at least one piezoelectric motor and the second piezoelectric motor at least partially overlap. Preferably, the motion periods of the at least one piezoelectric motor and the second piezoelectric motor is fully contained within the motion period of the other piezoelectric motor. Preferably, the motion periods of the at least one piezoelectric motor and the second piezoelectric motor coincide.
Preferably, the contact surfaces of the at least one piezoelectric motor and the second piezoelectric motor are displaced toward the flexible material during their respective periods of motion such that the material is pinched between the respective contact surfaces.
Alternatively the contact surface of the at least one piezoelectric motor is displaced toward the flexible material during the period of motion of the at least one piezoelectric motor and wherein the contact surface of the second piezoelectric motor is displaced away from the flexible material during the period of motion of the at least one piezoelectric motor. Preferably, the contact surface of the second piezoelectric motor is displaced toward the flexible material during the period of motion of the second piezoelectric motor and wherein the contact surface of the at least one piezoelectric motor is displaced away from the flexible material during the period of motion of the second piezoelectric motor, such that the at least one piezoelectric motor and the second motor alternately apply motion to the flexible material.
In a preferred embodiment of the invention the method includes:
(a) contacting a second contact surface of the at least one piezoelectric ceramic motor with a first side of the flat flexible material, said motor being operative to impart linear motion to surfaces which are in contact with the second contact surface; and
(b) providing a second bearing surface on a second side of the flat flexible material opposite said second contact surface.
As with the first bearing surface, the second bearing surface may be a roller or a contact surface of an additional piezoelectric motor. The additional piezoelectric motor preferably cooperates with the second contact surface in the same way as the second piezoelectric motor cooperates with the contact surface.
Additionally, in accordance with a preferred embodiment of the present invention, the piezoelectric ceramic motor has two upper and two lower electrodes and wherein the two upper electrodes are of the same size but different than the size of the two lower electrodes.